gas transport Flashcards
altitude sickness: explain the effects of altitude on oxygen availability, explain the acute and long term compensatory physiological mechanisms to high altitude, explain the pathophysiological cause of high-altitude pulmonary and cerebral oedema, and recall the first line interventions to treat altitude sickness
define hypoxia
specific environment with low PO2 (conditions)
define hypoxaemia
low PaO2 in blood
define ischaemia
tissues receiving inadequate oxygen
what can bring on hypoxic stress
altitude, exercise, disease (e.g. COPD)
what changes when low PO2 (still 21%) at high altitude and what detects this change
low PAO2 (alveolar) and low PaO2 (arterial), activating peripheral chemoreceptors (as opposed to central control using PCO2)
what outflow increased after low PaO2 detected
sympathetic nervous system
what 2 responses occur after increased sympathetic nervous system outflow
increased ventilation to increase alveolar oxygen and oxygen loading; increase cardiac output and heart rate to increase oxygen loading and tissue delivery
however what does hyperventilation lead to and what is the effect
hypocapnia, reducing central drive to breathe, reducing ventilation and hence oxygen loading
what does the CO2 loss cause
increased pH (alkalosis), shifting oxygen-dissociation curve left, increasing Hb affinity for O2 and causing decreased O2 unloading
what detects high pH
carotid bodies
what is the response to high pH
increased HCO3- secretion and causing kidneys to recover and manufacture more H+, normalising oxygen-dissociation curve to increase oxygen unloading
what does low PaO2 also increase
erythropoietin production, increasing erythrocyte production and oxygen unloading
why do oxidative enzyme/mitochondrial numbers increase
to allow for greater oxygen utilisation to provde energy
why is there a small 2,3-DPG increase
shift of oxygen-dissociation curve to right, increasing oxygen unloading
diagram of response to altitude
benjis
2 prophylaxis to high altitude
acclimation (stimulated by artificial environments e.g. hyperbaric chamber), acetazolamide (carbonic anhydrase inhibitor to accelerate slow renal compensation to hypoxia induced hyperventilation)
cause of acute mountain sickness
maladaptation to high altitude, with onset within 24 hours of ascent
pathophysiology of acute mountain sickness
mild cerebral oedema
symptoms of acute mountain sickness
nausea and vomiting, irritability, dizziness, insomnia, fatigue, dyspnoea
consequences of acute mountain sickness
HAPE/HACE progression (high altitude pulmonary and cerebral oedemas)
treatments of acute mountain sickness
stop ascent, analgesia, fluids, hyperbaric O2 therapy
cause of chronic mountain sickness
idiopathic
pathophysiology of chronic mountain sickness
secondary polycythaemia increases blood viscosity (higher Hct), so blood sludges through systemic capillaries, impeding O2 delivery
symptoms of chronic mountain sickness
cyanosis (bluish discolouration), fatigue
treatment of chronic mountain sickness
remain at low altitude
causes of high altitude pulmonary oedema
rapid ascent and inability to acclimatise
pathophysiology of high altitude pulmonary oedema
pulmonary vessel vasoconstriction in response to hypoxia, causing increased pulmonary pressure and permeability which exceeds lymphatic drainage
symptoms of high altitude pulmonary oedema
dyspnoea, dry cough, bloody sputum, crackling chest sounds
consequences of high altitude pulmonary oedema
impaired gas exchange
treatments for high altitude pulmonary oedema
descend, hyperbaric O2 therapy, nifedipine, sildenafil
causes of high altitude cerebral oedema
rapid ascent and inability to acclimatise
pathophysiology of high altitude cerebral oedema
cerebral vessel vasodilation in response to hypoxaemia; increased fluid leakage to cranium, compressing brain and raising intra-cranial pressure
symptoms of high altitude cerebral oedema
confusion, ataxia (poor-coordination), behavioural change, hallucinations, disorientation
consequences of high altitude cerebral oedema
irrational behaviour, irreversible neurologic damage, coma/death
treatments for high altitude cerebral oedema
immediate descent, hyperbaric O2 therapy, dexamethasone
